1. Field of the Invention
This invention relates to an ultrasonic method and device for the examination and detection of defects of aluminothermic rail welds. More specifically, the invention relates to the use of a set of phased array transducers disposed on different surface portions of a rail associated with phased array beamforming electronic and transducer positioning systems to assist with transducer manipulation.
2. Description of the Related Art
In a “continuous welded rail” (CWR) technique commonly practiced in Europe to improve the quality of ride for passenger trains, rail joints are welded in-situ welding of using thermit welding. In this process, a highly exothermic reaction between aluminium and iron oxides results in the production of molten steel which is poured into a mould surrounding a gap to be welded. The thermit welding process includes the following steps: preparation of the rail cross section, placing the mould, preheating the rail portions to be welded, and ignition of the thermit reaction.
The procedure of “controlled localized reaction” to keep the thermit mixture ignition under control was invented by Dr Goldschmidt and, hence, the process is sometimes also known as the Goldschmidt process. Individually patented processes have led to different trade names such as “Thermit,” “Boutte,” “Argothem,” etc.
Although aluminothermic welding is well proven for rails, it is none-the-less a critical safety component of the rail infrastructure. Yet these welds are not volumetrically inspected. According to European and British standards for railway applications BS EN 14730-1:2006, singles element ultrasonic transducers are used to inspect the rail welds at three different areas including head, web and ankle zones, each transducer is used to manually scan the corresponding surfaces with wedges shaped between 45 and 70 deg, this method is a highly time consuming operation and very operator dependent. Furthermore, single element transducers cannot be dynamically focused on defects when the transducer is moved, so the detection pertinence of the method is affected.
U.S. Pat. No. 3,960,005 to Vezina (hereinafter “Vez005”), discloses an ultrasonic testing device for thermit rail welds, including a longitudinal transducer shoe placed along the top surface of the rail and a plurality of single transducers to provide scanning of the rail depth. Vez005 also discloses an inclination of the transmit pulse of at least 45 degrees to address the depth of weld. Vez005 discloses detecting ultrasonic energy transmitted from different emitting transducers to indicate the ultrasonic transparency of the weld. This cannot be applied to the rail shoe inspection and, moreover, the method of Vez005 will work only on substantial size defects. No ultrasonic beam focusing is disclosed.
US Patent Application Publication No. US 2010/0307250 to Brignac et al. (hereinafter “Bri250”) discloses a weld inspection device for inspecting internal defects of rail. The device comprises attachment structures assembled together by rods which play a role of linear guidance for a runner that carries ultrasonic probes and can be moved longitudinally with a top surface of a rail. The inspection device described by Bri250 employs several transmitter/detectors modules to transmit and receive at different angles to provide a full set of data from the region of interest by moving the runner alongside the rail. Although not mentioned, for one skilled in the art the angled transducers as described by Bri250 are assumed to be wedged to provide such a feature. No indication of electronic focusing nor electronic beam steering is found. With respect to the Bri250 description, a rail's aluminothermit weld can be inspected from the head to the ankle with a best detection performance expected for flaws located in the web of the rail because the transducer lateral resolution will favour flaws located within a certain distance from the surface of transducer. Such a device will exhibit poor sensitivity and resolution in some areas of the weld (near the top surface and at the ankle), furthermore, the toes of rail cannot be inspected according to this disclosure.